(a) Field of the Invention
This invention relates to linear aromatic polymeric species, particularly polymers and oligomers and a process for their preparation.
(b) Description of the Prior Art
High molecular weight linear aromatic polymers which consist of aromatic groups joined by isopropylidene groups have attractive physical and chemical properties for use as engineering plastics. The preparation of such polymers from simple, readily available aromatic compounds such as cumyl chloride has not been successful as a result of side condensation reactions which terminate the polymerization.
High molecular weight polymers have been synthesized by a Friedel-Crafts alkylaticnreaction of 2-chloroisopropyl substituted aromatic compounds with other aromatic compounds; for example p-bis(2-chloroisopropyl) benzene has been condensed with diphenyl ether to yield a high molecular weight linear polymer. This polymerization, however, requires stringent reaction conditions including use of a special Friedel-Crafts catalyst typically consisting of nitrobenzene, tritylhexafluoroarsenate and aluminum chloride, low temperatures and a restricted group of solvents. The reaction must also be carried out in the absence of water and oxygen. The stringent reaction conditions required and the difficulty in obtaining highly purified monomers for the reaction have precluded further work on the process.
Transalkylation processes have also been developed employing perfluorinated resin sulfonic acids such as Nafion-H (trade mark) as catalysts. Thus dealkylation of a t-butyl substituted bisphenol in the presence of toluene as acceptor molecule produces t-butyl toluene and unsubstituted bisphenol.
Bisphenol A (4,4'-isopropylidenebisphenol) is manufactured by direct condensation of acetone with a large excess, typically 6 to 10 fold, of phenol in the presence of an acid catalyst, preferably an ion exchange resin. However, this condensation reaction is not quantitative enough to employ as a polymer forming reaction because side polyalkylation reactions and indane forming reactions act as terminating reactions, especially when the stoichiometry approaches 1:2 in the reaction. The synthesis is only successful when a large excess of phenol is used; but even when a large excess is used significant amounts of by-products are formed.